PowerMac G4 won't read DVD burned on Powerbook G4.

My Powerbook G4 (OSX 10.4.6) is running iLife 5. I just burned a DVD on it using iDVD. I tried to play the DVD on my PowerMac G4 (OSX 10.4.6) (which by the way is running iLife 6) and the drive won't recognize the DVD. The DVD plays fine in the Powerbook and also on the DVD players that I have in my home. I checked out the superdrive on the PowerMac by playing a CD and a commercial made movie DVD and it worked fine. The DVDs I'm using are Memorex DVD-R. Any idea what the problem could be?

Stu

PowerBook G4 Mac OS X (10.4.6)